With the increasing use of networks as typified by the Internet in recent years, the transmission and reception of e-mail and files has become widespread. In line with this trend, concerns have grown concerning security.
When electronic information is exchanged via a network, there is a possibility of contents being tampered with, rewritten, or switched, and such actions may leave no traces and be difficult to detect after the event. Moreover, it is comparatively easy to tap into a communication path and make use of a communication in progress. Hitherto, a method of achieving security by sending electronic information in encrypted form has been used in such cases. However, with an encryption method, all electronic information to be sent is included in the communication data, and therefore in the event of a communication leak, it is still possible for a highly skilled hacker to decrypt and tamper with electronic information.
Furthermore, the introduction of personal information protection legislation has involved organizations and institutions that handle personal information in enormous effort and expense in order to manage such information, since a heavy social responsibility is inevitably incurred in the event of an accident arising out of the handling of personal information. However, no matter how stringently management is implemented, mishaps related to personal information continue to occur.
Technologies for protecting personal information can be broadly classified as follows.    (1) User authentication: A system whereby a user accessing information is confirmed to be an authorized user at the entry point. A typical example is authentication by means of an ID or password. Biometric authentication techniques using physical characteristics such as fingerprints, vein patterns, and iris patterns, are also included in this category. This kind of technology prevents unauthorized access at the information entry point, but does not protect personal information itself once unauthorized access has been achieved. While falsification of biometric authentication data is difficult, drawbacks include high cost.    (2) Information encryption: A system that prevents persons other than the encryption key holder from learning information contents. Even when personal information is encrypted, it comprises an integral entity as information, and a possibility of information leakage remains through loss or theft.    (3) Thin client: In order to prevent leakage of information including personal information, a hard disk (HD) is not installed in a terminal personal computer from the outset, and data or software needed for work is accessed via a LAN.    (4) Information distribution: An item of information is divided into a plurality of distributed information items and managed in that form. The entirety of the information cannot be seen simply by viewing the individual distributed information items. An example of this technique is the information management system described in Patent Document 1, which attempts to achieve confidentiality and security of personal information by fragmenting personal information by means of division and storing the information in a plurality of data storage terminals in a network.
The personal information distributed management method and system described in Patent Document 2 presents a method whereby personal information and notification destination information located in distributed fashion in a plurality of terminals in a network is transferred among the terminals.    Patent Document 1: Unexamined Japanese Patent Publication No. 2003-271782    Patent Document 2: Unexamined Japanese Patent Publication No. 2004-178517